1. Field of the Invention
The present invention relates to a method for producing an electrical feedthrough in a substrate, and a substrate having an electrical feedthrough.
2. Description of the Related Art
Electrical feedthroughs in a substrate or in a subarea of a substrate, such as a wafer, for example, exist in numerous specific embodiments. The objective is always to achieve the smallest possible feedthrough at a low electrical volume resistance. To achieve this, frequently a narrow through hole having practically vertical walls is produced in the substrate in question, the wall is electrically insulated, and the through hole is then completely or partially filled with a metal or a metal alloy in order to obtain the desired low volume resistance.
Depending on the application, this known approach has limitations. On the one hand, there are applications in which the presence of metal results in interference. The micromechanical pressure sensor is named here as one example of numerous MEMS applications.
FIG. 3 shows a schematic cross-sectional illustration for explaining the object on which the present invention is based, with reference to a substrate having an electrical feedthrough and a pressure sensor as an example.
In FIG. 3, reference numeral 10 denotes a silicon semiconductor substrate. A first area 1 having an electrical feedthrough 6a and a second area 11 having a micromechanical component in the form of a pressure sensor are provided in silicon semiconductor substrate 2. Feedthrough 6a is connected to a first electrical contact terminal DK1 of pressure sensor 11 via a printed conductor 15a on front side V of substrate 10. Pressure sensor 11 has a diaphragm 3 which is provided above a cavity 3a. A piezoresistive resistor 4 and an insulation trough 4a situated therebeneath are diffused into diaphragm 3. First electrical contact terminal DK1 as well as a second electrical contact terminal DK2 contact piezoresistive resistor 4 in such a way that the piezoelectric resistance therebetween is detectable.
A first insulating layer Ii is provided between electrical metal printed conductor 15a and front side V of substrate 10. A second insulating layer 12 is provided between an electrical metal printed conductor 15b on the back side, and back side R of substrate 2. Insulating layers I1 and 12 may be oxide layers, for example. Feedthrough 6a connects printed conductor 15a on the front side to printed conductor 15b on the back side. A wall insulating layer 7a, which is likewise made of an oxide, for example, insulates feedthrough 6a from surrounding substrate 10. Lastly, reference numeral 9 denotes a so-called seed layer for applying the metal of feedthrough 6a, which at the same time may be used as a diffusion barrier.
In such classical micromechanical pressure sensors 11, deformation of silicon diaphragm 3, which is situated on silicon substrate 10, is measured via the piezoresistive resistor. The deformation of diaphragm 3, and thus the resistance signal of piezoresistive resistor 4, changes when the pressure changes. As a result of the different material parameters of silicon and metal, narrow metal printed conductors 15a located at the surface and in the vicinity of diaphragm 3 result in voltages which are transmitted via substrate 10 to diaphragm 3. The temperature-dependent portion of the voltages may be compensated for, with some effort. However, the inelastic properties of many metals also result in hysteresis in the characteristic curve of the pressure sensor. It is not possible to compensate for this effect. When metallic areas are provided not only at the surface but also at a depth in substrate 2, even greater adverse effects on voltage-sensitive components, for example such as pressure sensors, are expected.
On the other hand, there are a number of applications in which primarily also high voltages or also only high voltage peaks (ESD, for example) are to be conducted by a substrate or a subarea of the substrate via an electrical feedthrough. This is difficult using the approach described above. The etched through holes are usually insulated by oxide deposition. The achievable oxide thicknesses are greatly limited by the process control and the specific geometry. Therefore, the maximum electric strength is also greatly limited. In addition, the surface of the through holes, which are produced using a trench etching process or a laser process, is rather rough. This roughness causes electrical field peaks which likewise reduce the electric strength.
Alternative approaches without metals are not feasible in many applications, since the extremely low volume resistances which are often necessary are achievable only using metals.
A micromechanical component having wafer through-contacting as well as a corresponding manufacturing method are known from published German patent application document DE 10 2006 018 027 A1. A blind hole is introduced into the front side of a semiconductor substrate using a trench etching process, and the side wall of the blind hole is porously etched using an electrochemical etching process. The blind hole is filled with a metal plating and subsequently opened by thinning the semiconductor substrate on the back side.
A micromechanical component having wafer through-contacting as well as a corresponding manufacturing method are known from published German patent application document DE 10 2006 042 366 A1, in which metallic material is initially applied to a first area on the surface of the top side of a semiconductor substrate. The first area is designed in such a way that it leaves open a second area on the top side of the semiconductor substrate, which does not have the metallic material, and completely encloses this second area. A thermal step is then carried out which produces a first volume area within the semiconductor substrate having P+ or P++ doping. The thermal step results in a diffusion process in which metallic material diffuses from the top side to the bottom side of the semiconductor substrate. As a result of the diffusion process, the first volume area thus produced encloses a second volume area, which is preferably composed of the unaffected P-doped semiconductor material. To provide electrical insulation between the second volume area and the P-doped semiconductor material enclosing the first volume area, the first volume area is porosified using a suitable etching process.
German patent application DE 10 2010 039 339.4, which is not deemed a prior art, discloses the combination of a metallic punch as the feedthrough having a wide insulation ring. It is characteristic for this system that low resistances and a high electric strength as well as an efficient strain decoupling may be achieved. However, this approach allows only for relatively large TSVs (through silicon vias) and the manufacturing process is complex and expensive.